Multidisciplinary Reservoir Study for Pilot CO₂ Injection in Depleted Gas Reservoir

The increasing interest in CCS projects challenges the subsurface studies to overcome the structure of classic reservoir study, focused on field development. Within the framework of Ravenna Carbon Capture and Sequestration (CCS) hub, scopes of the project are:

• selection of the best candidate reservoirs and levels for CO₂ sequestration,

• injectivity and re-pressurization evaluation of the reservoir during injection,

• CO₂ plume evolution analyses, o geomechanical and geochemical assessment.

Eni recently completed a screening study to determine the CO₂ storage potential of gas-bearing fields in Southern Europe area. Reservoirs and levels were evaluated and ranked based on storage capacity, injectivity and number of existing wells. Preliminary 3D dynamic modelling evaluations on selected candidates were performed by using dedicated and history-matched compositional reservoir models, to account for CO₂ injection.

Once defined the final reservoir candidate, several scenarios were evaluated for a pilot injection project, optimizing injector's location based on CO₂ plume evaluation versus time. Moreover, specialistic studies were performed to predict caprock behaviour (Thermally Induced Fracturing, Cap Rock Integrity) and about the possible mineralogical precipitation/dissolution processes during and after the injection of CO₂. Numerical simulation results show that nor injectivity issues, neither geomechanical risks are forecasted for the planned pilot injection. All the outcomes of the integrated reservoir study were fundamental to speed up the road to the execution of the Company first-ever CO₂ pilot injector for CCS purposes.

The study shows an integrated methodology to assess reservoir storage capability; the study of CO₂ plume evolution versus time will help the other departments involved in the project to finalize monitoring techniques and to phase P&A operations, especially for the pilot phase of the project.

Carbon Capture and Storage (CCS) is a widely gaining popularity technology of capturing carbon dioxide from large industrial sources and sequestering permanently into deep underground geological formations. It is believed that CCS is the only applicable solution to reduce CO₂ emissions at the gigatons scale. Nevertheless, the application of CCS is not as straightforward as it appears, but things are changing very fast in these last years and several projects are going to see their birth.